Schlemm's canal cannulation may rejuvenate aqueous outflow

Key Points

"What if you could rejuvenate the outflow system in patients with glaucoma and restore healthy IOP without penetrating the eye, without creating a bleb or fistula, and without undue postoperative care?" Dr. Lewis asked. He is a cataract surgeon and glaucoma specialist practicing in Sacramento, CA.

Dr. Lewis explained that canaloplasty is an attempt to reestablish circumferential flow from the restored Schlemm's canal to the collectors and achieve a physiologically controlled IOP without the bleb and without developing bleb-related postoperative problems while using a standard surgical nonpenetrating approach.

The surgical approach starts with the creation of a standard half-thickness scleral flap. Beneath the flap, the surgeon locates the superficial area above the ciliary body to penetrate the canal and insert the cannula, which is passed through the entire length of the canal and out the other end, where a suture is tied to the distal end of the lighted beacon.

The cannula is then gently withdrawn, while viscoelastic (Healon GV, Advanced Medical Optics) is simultaneously injected to help dilate the canal and collector system. The 10-0 polypropylene (Prolene, Ethicon) suture is tied tightly so that the tension facilitates adequate outflow. The scleral flap and conjunctiva are then closed to prevent development of a bleb.

Dr. Lewis presented the most recent findings from a 12-month prospective study of canaloplasty that he and numerous colleagues are conducting in the United States, the European Union, and South Africa. Enrollment criteria included patients with open-angle glaucoma and, for this analysis, a preoperative IOP greater than 21 mm Hg.

Of 60 patients in this group, 12-month follow-up data were available for 16 when Dr. Lewis presented the findings. These patients had a 38% IOP drop, with an average IOP of 14.9 mm Hg.

"If you look at the success rate of these patients with IOP of less than 18 mm Hg, for those patients with unqualified success, we had a 76% success rate at 12 months and an 82% qualified success rate-that's with medications-at 12 months," Dr. Lewis said.

"There are some caveats to this procedure," he continued. "There's a learning curve, there's the extent of suture tension, and the issue of complications."

A learning curve

Addressing the learning curve, Dr. Lewis observed that many glaucoma surgeons have objected that locating the Schlemm's canal is too challenging.

"The reality is that, with good instruction, the canal is not difficult to find," he said. "The initial incision is made in the superficial flap in the sclera. A second inner flap is created anterior to the choroid, and the second inner flap is dissected up to the canal as it presents itself, which allows insertion of the flexible microcannula."

The second caveat is the role of suture tension, Dr. Lewis said. It was shown in a previous study that when there is minimal distention of the suture in the canal, the pressure reduction is insufficient. However, with adequate suture tension, the pressure declined to 13.8 mm Hg.

"Suture tension does play an important role in the outcome of this procedure," Dr. Lewis noted.

Regarding complications, 8.6% of the patients in this study experienced one or more incidents. The most common was a slight elevation of IOP on the first day postoperatively; others included hyphema, hypotony, and a Descemet's membrane detachment.

In contrast, the occurrence of complications was 57% in a recent study of trabeculectomy versus tubes, Dr. Lewis said. However, the patient population was different and the conditions were more complicated in that study.

"Canaloplasty is a nonpenetrating approach to glaucoma surgery utilizing circumferential flow that does not depend on the bleb. This procedure provides a very interesting and unique opportunity to work in a space that glaucoma surgeons have not worked in," Dr. Lewis said. "Not only does it provide an opportunity for surgical control of glaucoma, but it may provide an opportunity for medical treatment as well, in the long term."